* Watkins to replace Bruce Culpepper at end of year
* Watkins to also replace shale boss Greg Guidry (Adds details, background)
By Ron Bousso
LONDON, March 27 (Reuters) - Royal Dutch Shell's U.S. boss, Bruce Culpepper, will step down at the end of the year and be replaced by former Maersk Oil Chief Executive Gretchen Watkins, the company said in a statement on Tuesday.
Shell's head of unconventionals, Greg Guidry, who oversees the Anglo-Dutch company's shale production in North America and Argentina, will step down on June 31, when he will be replaced by Gretchen.
Watkins will retain her role as head of unconventionals when taking over as Shell U.S. country chair, the company said.
Shell, which has large offshore production and a number of refineries in the United States, has earmarked its shale business as a key growth engine for the next decade.
It aims to boost its overall shale production by 200,000 barrels of oil equivalent per day (boe/d) to 500,000 boe/d between 2017 and 2020, mostly in the United States with some production in Argentina, Guidry told Reuters in March.
North America accounted for roughly one fifth of Shell's total oil and gas production in 2017 and over one third of its refining capacity. (Reporting by Ron Bousso, editing by Louise Heavens and David Evans)